When 3H-uridine is injected into the eye of fish during regeneration of the optic nerves, large amounts of 3H RNA can be detected within optic axons and axonal growth cones as regeneratig fibers re-enter the optic tectum. Biochemical evidence suggests that a large fraction of this 3H-RNA is 4S RNA. It is likely that 4S RNA is synthesized in retinal ganglion cells and is then axonally transported into the growing fibers. This study investigates some of the characteristics of axonal 4S RNA in regenerating optic nerves of goldfish. The research proposed for this year (03) is as follows: 1) to determine the cellular distribution of 3H-4S RNA in the goldfish optic tectum following intraocular injections of 3H-uridine and at times up to 180 days after crushing the optic nerve. These experiments utilize EM autoradiographic techniques and attempt to determine whether 3H-4S RNA once axonally transported to the goldfish optic tectum remains in the axon or is transferred to surrounding cells. (2) To determine whether axonal 4S RNA can be aminoacylated by free amino acids supplied from the retina. These experiments will be performed by injecting labeled amino acids into the goldfish eye and isolating axonal 4S RNA. (3) A third set of experiments examines the axonal transport and transcellular transfer of nucleosides and polyamines during optic nerve regeneration and compares the findings with those obtained in intact fibers. The purpose of these experiments is to explore further the possibility that optic axons of the fish supply materials to periaxonal cells to be utilized by these cells in RNA and protein synthesis. The overall goal of these experiments is to identify the biochemical requirements of the growing axon; specifically regarding 4S RNA and its precursors. A better understanding of the biochemistry of regenerating may allow us to identify the reason(s) why mature axons in the CNS of mammals have lost their ability to grow while those of lower organisms retain this ability.